Industrial robots that pick up workpieces transported on a conveyor have been widely used in the field of factory automation (FA). Such robots are used to, for example, pick up workpieces being transported on a conveyor and place the workpieces into containers transported on another conveyor (commonly referred to as a pick-and-place operation).
Workpieces transported on a conveyor may overlap one another. When the robot picks up a lower one of two overlapping workpieces, the upper workpiece is affected by the movement of the lower workpiece and can change its position. In this case, the robot redetermines the position of this workpiece. One method for avoiding this is to eliminate overlaps between workpieces during transportation. Japanese Unexamined Patent Application Publication No. 2015-174758 (Patent Literature 1) describes a technique for eliminating overlaps between workpieces, or specifically describes a transportation device including conveyors that can eliminate various forms of overlaps between individually packaged bags during transportation. This transportation device uses an additional mechanism for eliminating overlaps between workpieces during transportation, and thus has a complicated structure.
Techniques for picking up workpieces without eliminating overlaps between workpieces during transportation have been developed recently. One such technique described in Japanese Unexamined Patent Application Publication No. 2012-055995 (Patent Literature 2) is a multi-articulated robot for picking up workpieces that are arranged without being placed on one another. The robot picks up a lower one of workpieces without moving an upper one of the workpieces. The multi-articulated robot described in Patent Literature 2 first moves a target workpiece by a predetermined displacement in a horizontal direction, and then picks up the target workpiece.